Finite element study of the penetration of an indenter into coated systems

The interplay of stress and strain and the load distribution along the contact area between indenter and the tested body are calculated for a coated system. Such a non linear elasto-plastic deformation process can be treated theoretically only by numerical means. This was performed by a very effective finite element program. Different two dimensional approaches to the common VICKERS microhardness test geometry will be presented: wedge and cone shaped indenters lead either to the uniaxial or the axial symmetric strain distribution. It is shown that friction forces between indenter and deformed material are not significant for obtuse-angled indenters. There is practically no relative movement along the contact interface and the deformation process is mainly characterized by embossed imprinting. No cutting of the material occurs even in thin films provided the indentation depth does not exceed film thickness too much. Load vs imprint depth diagrams for indentation and during subsequent load reduction are also presented and show the gradual take over of the test load by the substrate after the film is penetrated. They also show the influence of elastic re-deformation. The reliability of computed results is justified by their agreement with wedge hardness measurements on steel and gold solid samples.